Conventionally, a mechanism component (hereinafter referred to as a “terminal block”) into which a plurality of terminals are assembled in order to connect, branch, and relay wires has been used, and various terminal blocks of different sizes and types depending on the use, such as for control panels, switchboards, and printed circuit boards, are known (for example, JP H7-73913A). To connect wires or conductors provided at leading end portions of the wires (hereinafter, collectively referred to as “wires”) to terminals in these terminal blocks, a method of fixing a wire to a terminal by using a screw, a spring, or the like in a state in which the wire is crimped onto the terminal and thus electrically connecting the wire to the terminal is commonly used.
Among others, a method of fixing a wire to a terminal by using the restoring force of a plate spring has the feature that, for example, a situation in which the fixation is loosened due to vibrations and the like is unlikely to occur compared with a method of fixing the wire to the terminal by using a screw. Moreover, terminal blocks of a so-called push-in (or direct plug-in) type in which, with the use of a plate spring, the wire and the terminal can be connected to each other by simply inserting the wire into an opening portion of a housing have also been developed and have recently come into widespread use (for example, JP 2013-500547T).
FIG. 11 shows an example of a conventional terminal block that adopts the above-described method of fixing the wire to the terminal by using a plate spring. Also, FIGS. 12 and 13 are diagrams for illustrating insertion and removal of a wire into and from a terminal block shown in FIG. 11. A terminal block 9 has a housing 94, a substantially U-shaped terminal 93 that is provided along an inner wall within the housing 94 and that is open upward, a plate spring member 92, and a plastic deformation preventing portion 941 that is integrally formed with the housing.
Moreover, a wire insertion port 94a through which a wire 95 is to be inserted and a tool insertion port 94b through which a tool 98 is inserted when removing the wire are formed in an upper surface of the housing 94. An opening is formed in a bottom surface of the housing 94, and a conductor 96 is inserted from the outside of the housing through this opening.
The terminal 93 is formed of a plate-shaped member and is disposed abutting against the inner wall of the housing 94, and a connection surface 93a that is to be electrically connected to the inserted wire is formed facing the inside of the housing. Moreover, a connection portion 93b that is connected to the conductor 96 inserted from the outside of the housing is formed in a bottom surface portion of the terminal block 9.
The plate spring member 92 is formed by bending a band-shaped plate spring into a substantially V-shape, and is disposed such that one flat plate portion 92b abuts against an inner wall of the terminal 93 on a lateral side that opposes the connection surface 93a, a leading end portion 92a of another flat plate portion 92c abuts against substantially the middle of the connection surface 93a of the terminal, and a bent portion 92d of the V-shape faces diagonally upward of the housing.
The plastic deformation preventing portion 941 is a member that is located at substantially the center of the bottom surface of the housing and protrudes upward from the bottom surface to a predetermined height.
When connecting the wire 95 to the terminal block 9, a leading end portion 95a of the wire 95 is inserted through the wire insertion port 94a, and as shown in FIG. 12, the leading end portion 92a of the plate spring member 92 is pressed by the leading end portion 95a against the restoring force of the spring so as to widen a gap between the terminal 93 and the leading end portion 92a of the plate spring member 92, and thus, the leading end portion 95a is pushed into the gap. Then, due to the restoring force of the leading end portion 92a of the plate spring member 92, the leading end portion 92a presses the leading end portion 95a of the wire 95 against the connection surface 93a of the terminal and thereby fixes the wire 95. As a result, the wire 95 is connected to the terminal 93, and if a force in a withdrawal direction is applied to the wire 95, an edge of the leading end portion 92a of the plate spring member 92 bites into the surface of the leading end portion 95a of the wire 95, so that the wire 95 is prevented from being removed.
When detaching the wire from the terminal block 9, as shown in FIG. 13, the tool 98, such as a slotted screwdriver, is inserted through the tool insertion port 94b of the housing 94, and the flat plate portion 92c of the plate spring member 92 is pushed downward against the restoring force of the spring to separate the leading end portion 92a from the wire 95. As a result, the wire 95 is released from the plate spring member 92 and can therefore be removed (detached) from the terminal block 9.
It should be noted that during insertion of the wire 95 as well, when the leading end portion 95a of the wire cannot be pushed in for insertion due to a lack of rigidity, the plate spring member 92 is pushed downward in the same manner as in removal of the wire, and in this state, even a wire that is not rigid, such as a stranded wire, can be inserted.
Moreover, when the plate spring member 92 is pushed downward by a tool as described above, deformation of the spring is restricted within a predetermined range by the plastic deformation preventing portion 941. Thus, the spring can be prevented from exceeding the elastic limit of the spring and plastically deforming due to excessive force being applied to the spring during insertion of a tool.
JP H7-73913A and JP 2013-500547T are examples of background art.
Incidentally, in the case where the strength of the above-described plastic deformation preventing portion 941 is insufficient, if a force at or above a predetermined level is applied to the plastic deformation preventing portion 941 when the tool is inserted and pushes the spring downward, the plastic deformation preventing portion 941 may be damaged and lose the function of preventing plastic deformation of the spring, and hence, the terminal block itself can no longer be used.
Conventional members for preventing plastic deformation, such as that described above, are often molded out of a synthetic resin. Therefore, if an attempt to achieve a smaller and slimmer terminal block is made, sufficient strength of the plastic deformation preventing portion cannot be obtained. On the other hand, if an attempt to obtain sufficient strength is made, the size of the plastic deformation preventing portion increases, and thus, a problem arises in that the degree of freedom of design of other members decreases. Moreover, if the plastic deformation preventing portion is composed of a metal or the like that is separate from the housing, the manufacturing cost increases.